Download Cardiovascular Dynamics Highlights File

More Cardiovascular Dynamics
Highlights from Lab
For Bio 260 from Marieb
Some Interesting Topics
• Review of Blood Pressure
• Tissue Perfusion (Blood Flow to tissues)
• Bulk Flow (Fluid Movements & Capillary
Dynamics)
• SHOCK
Monitoring Circulatory Efficiency
• Vital signs: pulse and blood pressure, along
with respiratory rate and body temperature
• Pulse: pressure wave caused by the expansion
and recoil of arteries
• Radial pulse (taken at the wrist) routinely used
Superficial temporal
artery
Facial artery
Common carotid
artery
Brachial artery
Radial artery
Femoral artery
Popliteal artery
Posterior tibial
artery
Dorsalis pedis
artery
Figure 19.12
Measuring Blood Pressure
• Systemic arterial BP
– Measured indirectly by the auscultatory method
using a sphygmomanometer
– Pressure is increased in the cuff until it exceeds
systolic pressure in the brachial artery
Measuring Blood Pressure
• Pressure is released slowly and the examiner
listens for sounds of Korotkoff with a
stethoscope
• Sounds first occur as blood starts to spurt
through the artery (systolic pressure, normally
110–140 mm Hg)
• Sounds disappear when the artery is no longer
constricted and blood is flowing freely
(diastolic pressure, normally 70–80 mm Hg)
Variations in Blood Pressure
• Blood pressure cycles over a 24-hour period
• BP peaks in the morning due to levels of
hormones
• Age, sex, weight, race, mood, and posture may
vary BP
Alterations in Blood Pressure
• Hypotension: low blood pressure
– Systolic pressure below 100 mm Hg
– Often associated with long life and lack of
cardiovascular illness
Homeostatic Imbalance: Hypotension
• Orthostatic hypotension: temporary low BP
and dizziness when suddenly rising from a
sitting or reclining position
• Chronic hypotension: hint of poor nutrition
and warning sign for Addison’s disease or
hypothyroidism
• Acute hypotension: important sign of
circulatory shock
Alterations in Blood Pressure
• Hypertension: high blood pressure
– Sustained elevated arterial pressure of 140/90 or
higher
• May be transient adaptations during fever, physical
exertion, and emotional upset
• Often persistent in obese people
Homeostatic Imbalance: Hypertension
• Prolonged hypertension is a major cause of
heart failure, vascular disease, renal failure,
and stroke
• Primary or essential hypertension
– 90% of hypertensive conditions
– Due to several risk factors including heredity, diet,
obesity, age, stress, diabetes mellitus, and
smoking
Homeostatic Imbalance: Hypertension
• Secondary hypertension is less common
– Due to identifiable disorders, including kidney
disease, arteriosclerosis, and endocrine disorders
such as hyperthyroidism and Cushing’s syndrome
Blood Flow Through Body Tissues
• Blood flow (tissue perfusion) is involved in
– Delivery of O2 and nutrients to, and removal of
wastes from, tissue cells
– Gas exchange (lungs)
– Absorption of nutrients (digestive tract)
– Urine formation (kidneys)
• Rate of flow is precisely the right amount to
provide for proper function
Relative crosssectional area of
different vessels
of the vascular bed
Total area
(cm2) of the
vascular
bed
Velocity of
blood flow
(cm/s)
Figure 19.14
Autoregulation
• Automatic adjustment of blood flow to each
tissue in proportion to its requirements at any
given point in time
• Is controlled intrinsically by modifying the
diameter of local arterioles feeding the
capillaries
• Is independent of MAP, which is controlled as
needed to maintain constant pressure
Intrinsic mechanisms
(autoregulation)
• Distribute blood flow to individual
organs and tissues as needed
Extrinsic mechanisms
• Maintain mean arterial pressure (MAP)
• Redistribute blood during exercise and
thermoregulation
Amounts of:
Sympathetic
pH
O2
Metabolic
a Receptors
b Receptors
controls
Amounts of:
Nerves
Epinephrine,
norepinephrine
CO2
K+
Angiotensin II
Hormones
Prostaglandins
Adenosine
Nitric oxide
Endothelins
Myogenic
controls
Stretch
Antidiuretic
hormone (ADH)
Atrial
natriuretic
peptide (ANP)
Dilates
Constricts
Figure 19.15
Long-Term Autoregulation
• Angiogenesis
– Occurs when short-term autoregulation cannot
meet tissue nutrient requirements
– The number of vessels to a region increases and
existing vessels enlarge
– Common in the heart when a coronary vessel is
occluded, or throughout the body in people in
high-altitude areas
Blood Flow: Heart
• During ventricular systole
– Coronary vessels are compressed
– Myocardial blood flow ceases
– Stored myoglobin supplies sufficient oxygen
• At rest, control is probably myogenic
Blood Flow: Heart
• During strenuous exercise
– Coronary vessels dilate in response to local
accumulation of vasodilators
– Blood flow may increase three to four times
Fluid Movements: Bulk Flow
• Extremely important in determining relative
fluid volumes in the blood and interstitial
space
• Direction and amount of fluid flow depends
on two opposing forces: hydrostatic and
colloid osmotic pressures
Hydrostatic Pressures
• Capillary hydrostatic pressure (HPc) (capillary
blood pressure)
– Tends to force fluids through the capillary walls
– Is greater at the arterial end (35 mm Hg) of a bed
than at the venule end (17 mm Hg)
• Interstitial fluid hydrostatic pressure (HPif)
– Usually assumed to be zero because of lymphatic
vessels
Colloid Osmotic Pressures
• Capillary colloid osmotic pressure (oncotic
pressure) (OPc)
– Created by nondiffusible plasma proteins, which
draw water toward themselves
– ~26 mm Hg
• Interstitial fluid osmotic pressure (OPif)
– Low (~1 mm Hg) due to low protein content
Net Filtration Pressure (NFP)
• NFP—comprises all the forces acting on a
capillary bed
• NFP = (HPc—HPif)—(OPc—OPif)
• At the arterial end of a bed, hydrostatic forces
dominate
• At the venous end, osmotic forces dominate
• Excess fluid is returned to the blood via the
lymphatic system
Arteriole
Venule
Interstitial fluid
Net HP—Net OP
(35—0)—(26—1)
Net
HP
35
mm
Capillary
Net
OP
25
mm
NFP (net filtration pressure)
is 10 mm Hg; fluid moves out
Net HP—Net OP
(17—0)—(26—1)
Net
HP
17
mm
Net
OP
25
mm
NFP is ~8 mm Hg;
fluid moves in
HP = hydrostatic pressure
• Due to fluid pressing against a wall
• “Pushes”
• In capillary (HPc)
• Pushes fluid out of capillary
• 35 mm Hg at arterial end and
17 mm Hg at venous end of
capillary in this example
• In interstitial fluid (HPif)
• Pushes fluid into capillary
• 0 mm Hg in this example
OP = osmotic pressure
• Due to presence of nondiffusible
solutes (e.g., plasma proteins)
• “Sucks”
• In capillary (OPc)
• Pulls fluid into capillary
• 26 mm Hg in this example
• In interstitial fluid (OPif)
• Pulls fluid out of capillary
• 1 mm Hg in this example
Figure 19.17
Circulatory Shock
• Any condition in which
– Blood vessels are inadequately filled
– Blood cannot circulate normally
• Results in inadequate blood flow to meet
tissue needs
Circulatory Shock
• Hypovolemic shock: results from large-scale
blood loss
• Vascular shock: results from extreme
vasodilation and decreased peripheral
resistance
• Cardiogenic shock results when an inefficient
heart cannot sustain adequate circulation
Acute bleeding (or other events that cause
blood volume loss) leads to:
1. Inadequate tissue perfusion
resulting in O2 and nutrients to cells
2. Anaerobic metabolism by cells, so lactic
acid accumulates
3. Movement of interstitial fluid into blood,
so tissues dehydrate
Chemoreceptors activated
(by in blood pH)
Major effect
Baroreceptor firing reduced
(by blood volume and pressure)
Initial stimulus
Physiological response
Signs and symptoms
Result
Hypothalamus activated
(by pH and blood pressure)
Brain
Minor effect
Activation of
respiratory centers
Cardioacceleratory and
vasomotor centers activated
Heart rate
Sympathetic nervous
system activated
Neurons
depressed
by pH
ADH
released
Intense vasoconstriction
(only heart and brain spared)
Central
nervous system
depressed
Kidney
Renal blood flow
Adrenal
cortex
Renin released
Angiotensin II
produced in blood
Aldosterone
released
Rate and
depth of
breathing
CO2 blown
off; blood
pH rises
Tachycardia,
weak, thready
pulse
Skin becomes
cold, clammy,
and cyanotic
Kidneys retain
salt and water
Water
retention
Urine output
Thirst
Restlessness
(early sign)
Coma
(late sign)
Blood pressure maintained;
if fluid volume continues to
decrease, BP ultimately
drops. BP is a late sign.
Figure 19.18